site-packages pollution with testing and tests subdirectories

After installing flufl.i18n 3.1 from PyPI into a virtual environment, we see pollution of the site-packages directory:

% ls /tmp/vv2/lib/python3.8/site-packages/
__pycache__/			flufl.i18n-3.1-py3.8.egg-info/	setuptools/
atpublic-2.0.dist-info/		pip/				setuptools-49.2.1.dist-info/
easy_install.py			pip-20.2.1.dist-info/		testing/
flufl/				pkg_resources/			tests/
flufl.i18n-3.1-py3.8-nspkg.pth	public/

testing and tests must not end up there.